Treatment of superphosphate



Nov... 15, 1938.

w. H. GABELER ET Al.

TREATMENT OF SUPERPHOSPHATE 2 Sheets-Sheet l Filed Deo. 11; 1955 Nov. 15,1938. w. H .LER ET A1. 2,136,793

` TREATMENT OF SUPERPHOSPHATE FiledDeo. ll, 1955 2 Sheets-Sheet 2 fj Planted' Nov. 1s, 193s f t-v' u v 1 i y ,'fidlf2,16l,793y I[UNITEDSTATI-:s .PATENT *OFFICE TREATMENT or surnnrnosm'rn `William Harold Gabelcr, Alvin Chcsley Wilson,

' Thomas Orkney Tongue, and Mark Shocld.

Baltimore, MdL, assignors, by mesne aiisignments, to The Davison Chemical Corporatioma l corporation of Maryland Application December 11, 1935, Serial Nm 53,999

8 Claims.

This invention relates'in general to the production of fertilizer fromphosphatic rock, and more `particularly toan improved method of manufacturing superphosphate `by itself or in ad'mixturel with other fertilizer ingredients.

The usual method"of manufacturing super-v phosphateis by these-called Den process.` This involvesbatch mixing of groundjphosphate rock and sulphuric lacid in a pan mixer. After a 10 relatively-.short mixing time the batch While still in av uid'o'r semi-fluid condition is dumped into a confined space called a Den. In some cases the mixing of ground rock and acid is made continuouslyv in la horizontal trough mixer.V `The Den may v*either bestationary or movable as in "mechanical `Dens.,. The fresh superphosphate is allowed tolset up in the den to a relatively soft solid mass.` In caseofstationary Dens themass c is dugout` by means of acrane` bucket and den) livered to la curing pile. In some places the fresh super-phosphate is rasped before being putV on the curing pile. The ra'sping operation ini volves feeding the fresh superphosphate past rapidly revolving'arms or knives which disintegratethe mass and aerates it. The purpose of this operation is to effect moistureelimination. In case of mechanical Dens the block of fresh superphosphate is always fiaked or shaved oil and aerated before yit'goes to the storage or curing pl1e. `The practice has always been to use as strong acid as possible for the acidulation to reduce the amount of water in the superphosphateas much as possible. The purpose of the flakingand aeration is also largely to reduce the moisturel content. The fresh superphosphate` made with as'strong acid as possible and frequently (after subsequent aeration is placed on -the curing pile where it remainsl for a period of generally not less than one month and ordinarily 40 three to fourzm'onths. The purpose of the curing period is to improve the physical, condition of the superphosphate and to allow the chemical .re-

action to go to-substantial completion This rey l duces the insoluble P205 and the free acid and conversely the proportion of available P205` is increased.' i l Y i If the superphosphate is to be sold for direct applic tion to the ysoil it is necessary to further treat he cured acid phosphate to improve its physical condition so that it will not set or cake in bags or causebag rot, and so that it will handle'stisijactorily through'a fertilizer 'drill.

- This is oidinarilyaccomplished by adding ground i phosphate rock or ground dolomite or lime and sand or ground limestone and'sand. This mixture is milled and screened landyput in storage. During this storage of' from 'two -w'eeks' to'a month a certain amount `of caking or set `takes place. The material `is milled and screened t 6o, again 'and is then'ready for shipment in bags or (Cl. 'i1-40) bulk.' This treatmentfreduces thefree acid and i improves the physical condition, .whichy although still far from ideal is acceptedby the trade.

goods orv so-called complete fertilizergthecured superphosphate is dry mixed with other fertilizer ingredients and allowed to cure. During. this: y y curing the mixture sets or cakes. `After 'a' cer- If the superphosphate is to be" soldl as mixed'v `prove the physical' condition. lThisI is a ycostly addition as the unit cost of nitrogen'in organics is about `two to three times asexpensive as in l inorganica. 'Ihe fertilizer value 'er-the organics, l

is generally less than 4the inorganics,` so the vreal purpose of the addition` of organicsis to improves 'v the physical condition of thefertilizer= All fertilizers are sold on guaranteed chemical analysis, so that the only commercial difference f' V between any fertilizers of identical {chemical composition is a difference in physical condition.

The criterion on physical condition,is,in turn the free flowing and free drilling qualities of the fertilizer. A truly free owingl fertilizer consists of dry. hard, discrete granules of substantially,`

Uniform Size. no dust and no oversize,-4 thus no segregation possible. i 'I'he term curing is soluble P205 or improvement in physical condi'- vsriousiy used in the rer! y tilizer trade, referring either to reduction in inf t tion and very often includes both. For thepur-f `p ose of describing this invention accurately and clearly we will l'denne theword curing as a re- 'duction of insoluble P205 only.` and will so use in physical condition we will so state. V- A primary object of this invention vision of a method which substantially elimithis term both in the remaining speciilcation andl i in the claims. When we refer to improvement l isthe pro-` l 4- nates the storagetime required for acidphosy phate and entirely eliminates the preliminary,

storage of complete fertilizer, and whichl willv rapidly reduce the insoluble P205 both' in superphosphate `,and in complete fertilizer and also to a greater extent than' has been possible heretoy-'j fore; thus effecting'economy onvmaterials. j

Another object of uns invention is to .produce superphosphate and Acomplete fertilizerof im proved physical condition Iof the characterv of porous', discrete, nodular*` encrusted and indurated globoid particlesin. a simple andmore ecos" nomical manner.

The invention has roriurther objects e ine-thee. which eliminates the necessity for cutting supere4 phosphate and putting it through a milling and screening operation twice to improve its Physical condition for direct application to the soil, and

' 2 .l which win produce a complete fertiliser' in of exemplincation. a preferred formand manner in which the invention may be embodied and practiced, but'without limiting tbe claimed lnvention lspecifically to such illustrative instance or instances.' Figure I is a side of apparatusadapted to carry out our process.

Fig. II is a diagrammatic view of another appar ratus dor carrying out the invention.

Figs. III, IV, `V and VI are lihlstrative-curve sheets showing velocities of curing reaction and reduction of free acid.

As vhas been previously described, the practice 'in the pastl during' manufacture of acid phosphate from phosphate rock hasbeen to use-as 'strong acid as' possible as well as to aerate .the

fresh superphosphate to reduce the moisture conv d approximately 7 to 8 R. P. M. and the drier i0 tentt'o a minimum. ,We .have made the surprising discovery thst` by going in exactly opposite direction, that adding a small amount ofiwater to silpel'phos-y .phate, made in the regular manner, and agitatins itfat atmospheric pressure and temperature to` preliminarily nodulize the superphosphate and.

directly thereafter, without intermediate storagecuring, removing the excess water from the preliminarily nodulized superphosphate -by drying with beat while agitating it at atmospheric pressure, a most remarkable increase lin curing rate Y as well as improvement in physical condition is obtained. Thus, instead of aerating the superphosphateto remove moisture, we actually malntain high -moisture or d moistin'e and operate at atmospheric pressures preliminarily nodulise itby tumbling to form discrete. nodular. firm particles before heating to dry the nodules dnd Y then directly subject thesel nodules to Y while tumbling until converted to discrete, nodu- "lar, encrusted and lndurated globoid particles.

'Inmaking complete fertiliser by meam of this invention. the preferred method is to mix superphosphatewith other fertiliser ingredients. meisten and agitate the mixture to noduliae it and directly thereafter remove excess'molsture from the pre-formed nodules by heating it as aforesaid.. 'An even more distinct curing eifect is obtainedthan incase of straight superpuesphate and an'improvement in physical condition to the extent that an ideal complete' fertillnr is obtained. r

, Referring to Pig. I. a crane bucket l delivers fresh superphospha out of the den. or partly cured den superphosphate. to feed hopper 2. An apron conveyor I made of slats deliversthesuperphosphate to a horizontal rotary cylinder '22. whiclifis operating in room temperature and at atmospheric pressure with a substantial nondrying atmosphere and is set'on a slight pitch and provided with lifting vanes l to agitate or tumble the material and thereby agglomerato it into fdiscrete firm nodules. l'br simplicity this cylinder will beereferred .to as the conditioner.

The lifting vanes l extend about one-fourth of the length of cylinder 22 from its upper inlet elevational view ofso-ne .type

aise-,rea

end. The cylinder 22 is about 3% feet in diameter, and about ten vanes or flights, approximately ve inches high, distributed around the inner circumference of the4 first quarter of the cylinder suiilce to initiate the agglomeration acdirect heat rotary drier operating at atmospheric pressure and provided with lifting vanes ii to agitate or tumble the material like the conditioner 22. An oil burner I2 feeds a fire box i3 lined with lire-brick and having a refractory balle wall; il for introducing hot combustion gases intothe drier Iii to heat the nodules to a temperature of about 180 F. An exhaust fan il `and stack I'I deliver the combustion gases to the atmosphere. Ii8 is a preliminary storage-pit. from which cranebucket I removes the treated material to storage. A swinging gate I9 allows the material to fall into the'plt i8 without admitting air into the outlet end box 20 oi' the drier.

The conditioner 22 is operated at a speed of about the same. The conditioner 221s about 3% feet in diameter and l5 feet long, whereas the drier is 3% feet in diameter and 30 feet long',

providing a capacity of about 100 tons of iinished material per 24 hours.

The 1superphosphate is fed continuously into the conditioner 22 at a uniform r'ate by means of feeder I. Thepurpose of the conditioner 22 is to agitate and agglomerate the superphosphate into yrelatively flrm discrete nodules, like pellets or ballspof more or less uniform. size before the nodulesare subjected to drying. The conditioner lsopen at both ends so as to'maintain a substantially non-drying atmosphere therein, that is, an atmosphere whose temperature and humidity is such relativel to the temperature and moisture' phosphate but also the age of the superphosphate,

that is, whether or not it is taken directly out of the den or has first gone to an auxiliary intermediate storage. We have also found that the particle sise of the nodules of 'agglomerated superphosphate issuing from the discharge end of the conditioner 22 is a function of the quantityv of water addition. The nodulized superphosphate drops as discrete firm-particles continu- .ously from chute 2i directly into the drier. In the drier the pellets are further tumbled while progressing continuously therethrough as .they

moisture content of the original super'- are being heated and dried at atmospheric pres.

sure-by direct contact with the heating gases `whichprovide a drying atmosphere and the pelletsn furiherfhardened to porous. discrete, en-

crusted and indurated nodular globoid particles whence they are discharged from the drier. The

byme'ans of crane bucket i. I.

The material is to stayin storage for `dried material is removed to storage from pit I8 K 2,136,793 v j a period of from only 2 to 3 days up to a week.

During this period the pellets get very much and'then immediately dried in drier lli.v The nodule material from the drier I analyzed as harder and have a crushing strength in excess follows:

of several times as great as fully cured ordinary Moistur, 7 72 den superphosphate. The material is then milled Total Pans 19'80 and screened and is ready for shipment.l By Insomma Pm 152 properly regulating the moisture content in the Available Pam. 18-28 conditioner the quantity of over-size that has Free acid V 476 to be disintegrated is reduced to a minimum. If l there is a tendency to form Iinesrin the final To more clearly illustrate the effect of the preproduct the ratezof water meinenV in the conai- `liimimur nodulizing and immediately following tioner is increased and if there `is a tendency to drying Opelstlns We refer t0 Curve sheet Fig III- forman excessive amount of over-size the water Curve (a) represents the 1301121011 Of the Superrate is reduced. phosphate of theabove composition and aged We have also discovered that while especially in curing piles. The insoluble P205 has been fresh superphosphate, when nodulized with too given as a ratio of the insoluble P205 over the great a quantity of` water, will form rather large total P205.- 'I'his is for the purpose of making l agglomerations of `from hazel-nut to fist size and w the curves truly representative as, to the efficiency l even larger, nevertheless on passing through the of conversion of insoluble P205 to available form. Y direct heat drier these larger agglomerations The insolublehas been plotted against time. In break down into smaller pellets. Thenodules this manner any apparent. Variation in insoluble while firm are insuch instances of such physical lP205 due to variations in water content both condition that'if taken out at the discharge end "free and xed is eliminated. I In other words. if of the conditioner and put in a small pile, the the insoluble P205 read of! the chart is deducted separate discrete particles or .nodules will tend from 100, the resulting gure represents the perto run together and form a claylike mass of the `centage of .acidulation or conversion of the P205 consistency of soft `modelers clay. from insolubieto available form. Curve (c) rep- Generally speaking in such instances the quan- `resents the above superphosphate treated `by tity of water added is decreased and we prefer to means of our process. l `regulatethe water addition so that the granules lCurve sheet Fig. IV represents `the free acid l leaving the conditionerlz are in such physical: reduction plotted against, time. Curves (a) and condition that they do `not immediately coalesce (C) correspond t0 the same letters in Fig-,IIL

if removed from the conditioner 22 and allowed to AS a further eillilstlatiOl! We, give below the stand stationary in a pile before entering the analysesof bothsuperphsphates 12 days old. drier I0. At least the tendency is not to run to- Y gether into one'clayey mass although there is ,Regular Treated some coalescence at the contact points of the firm su' sugegos granules. I

In addition to'this the moisture content is also regulated in accordance with the size of the mateijl il 231g rial issuing from the drier `so that when screen 50u e I l l r tested about two-thirds to three-fourths does fglfffj' lg not need to be crushed, that is over '70% will pass i through an 8-mesh screen and most of the rest To show that our process is also eilective on will pass through a .fi-,mesh screen. superphosphate that has stayed in the storage We will now give some specic examples of op pile for some time another 100 ton pile of regular erating conditions and products produced in ac- 'superphosphate was set aside. The analysis of cordance with our invention as well as comparathis material when made and 12 days old was as tive results of producing superphosphate in the follows: A Y Iold manner. I

A quantity of tons den superphosphate was Fm'h 12 days 01d made up in the usual manner. This superphose Y l phate was made from 72.9% B. P.- L. Florida rock` and 55 B. sulphuric` acid. i. The actual batches l txiulrf: "I: islet 13.32 used in the mixing pan were as follows: 3: 1232i g- Pounds Free acid... 10.00 eos yCiround rock 1125 u e 55 B'. vfwiile 1071,l This-12 day old material was moistened in the conditioner with 6.7% water l and nodulized wig? Superphospbate @ken out Orf the @en apa thereim The treated material immediately after e A Per ent direct treatment in the drier land after 3 days Moisture 10.29 analyzem i i Y Total P205 19.68 Insoluble P205 2.07 Treated material Available P205 17.61 l i. Free acid '1,55 Immediate Sdays The above determinations weremade according to..the A. o. A. C. voilicial methods, except the ftfgjjjjjjjjjjj; 221g $13,# free acid, for which ,there is no official method. P10' n1)- The free acid was determined as yHaPOi by the mammie` 4144 218e tentative A. 04. A. C. alcohol method. e

Slipelphosphate of the above l composition was The regular superphosphate 24 days after makpromptly thereafter moistened by the addition of jing and the treated superphosphate 12 days after 2.2% water and nodulized in the conditioner 22` the treatment (which corresponds rto 24 days from the initial superphosphate) analysed as follows: n

Untreated Treated am 4. 4o

sos au l This is representedgraphica1ly in curve sheets Hgs. V and VI. where curve (a) represents the ytory physical condition, because it was substantially all in the form of ilnes.

The preliminary nodulizing operation in itself improves the curing. In conjunction with. the

' directly following drying operation, however, the

regular superphosphate and curve (c) the treated superphosph'ate as described above. For the purpose of preparing all the curve sheets the piles of materials were resampled and analyzed every few days. The curves represent mean or average results;

We are not able to deiinitely-state why the above beneficial results are obtained. Merely as a theory and without binding ourselves thereto, we suggest the following explanation.

The. free acid in superphosphate is substantially always HsPOi.' If any H2804 is present it is only in traces. The wetting and nodulating ot lthe superphosphate may redistribute this phosphoric acid and may likely cause some hydrolysis of the monocalcium phosphate. On drying, the acid` is concentrated and this as well as the elevated temperature of the material in the-drier (about l80l".) facilitates the attack of the free phosphoric acid on the insoluble P205. It may be mentioned at this point that with strong phosphorlc acid the acidulating reaction ,is faster than` with weak phosphoric' acid. This is in contradiction to sulphuric acid. Ii sulphuric acid is used for the-original acidulation in a strength oi" 60 B. or higher, the acidulatlng reaction is largely inhibited.

The attempt to dry superphosphate to improve its physical condition is old and the material produced is substantially nnely powdered and there is no curing. More often there isan actual reversion of P205, ,that is an increase of insoluble P20. It is the nodulizing operation at room tcm-A perature andatmospheric pressure preliminariiy but in conjunction with the directly following drying operation at atmospheric pressure which beneiicial result is vastly improved.

An example of only nodulizing the superphos-l phate with 1.9% of water is as follows:

Original Nodulized Super' Super' phosphate phosphate Moisture 9. 14 1l. 04 Total PgO 2l. 00 l9. 58 insoluble 130;. i180 1. 58 Available PO; 18. 20 18. 00 Fna acid. 8. 03 5. 87

It the superphosphate'is made originally with a sudiciently high moisture content it is nodulized withoutwater addition. The following supcrphosphate was nodulized without water addition:

Moisture 12.32 Total Pam 19.25 Insoluble P205' 3.06 Available Pzs 16.19 Pme scid- 11.11

It i's to be understood that we .dol not limit our invention in all itsaspects tothe particular kind oi conditioner described for the nodulizing step. We may for instance use a pug mill. consisting of a horizontaltroughmixer provided with a horizontal shaft with blades or arms set at a suitable angle. 0n the other hand we may use a dough mixer with sigma blades. Further, we may for examplev use a Chilean mill as the conditioner.

In the previously given examples the moisture' vcontent oi the treated isuperphosphate has been reduced below the moisture content of the original produces the beneficial results both as to curing as to physical condition. ,i As an example of large scale drying tts (dry-' ig only without the `preliminary nodulation) onY f superphosphate we give the following ior a direct 4The dried material was not nodular but very dusty and .thus unsatisfactory from the standpoint of physical condition.

Beton drying Altar drying 19.(X). HN

untreated material. Although we prefer to bring the moisture content down-to about 5%, this is not necessary for the purpose of realizing beneilcial results by our invention. We have for instance taken superphosphate of 9% and nodulined this material with a water addition of lll/2% subsequently drying the ilrm nodules to the original 9% moisture. After one day the pellets produced were hard and ot excellent physical' condition. This brings out a point ot our process that it is 'not necessarily dependent upon a moisture reduction of the. original superphosphate. We have no delinite explanation as to why this happens. yAs a theory, it may be that the nodulation step lbrings the individual particles of superphos phate in close contact with each other and that subsequent recrystallixing phenomena set the material Vto hard. and, to all appearance, dry pellets without necessarily showing a lower moisture content by analysis than the original superphos- -phate. The results ot the product emphasize the fact that the invention not only improves the curing or the chemical analysis of the superphosphate, but also produces a superphosphate of greatly superior physical condition.

As has -been previously set forth, the nodulation operation may or may not require water addition to the superphosphate. It is further to be understood that instead of adding water other phosphoric acid, potassium chloride, potassium wetting agents may be used in the nodulation step, as for instance, water solutions of sulphuric acid,

sulphate, sodium-nitrate. In case water solutions of acids are used in the nodulation step, a certain the superphosphate asv it is being -nodulized or before it lis nodulizedf:l This will furnish addit tional available P-10s.

offor instance potassium chloride, yn-ar'nount` of phosphate rock is also added. This :will-be referred to morespeciiically in subsequent `In using a water solution a small descriptionl of making complete fertilizer by Moreover, in `nodulizing superphosphate withv out water addition we may'for instance take the fresh acid phosphate made by mixing rock and acid and treatthis in our nodulizing step withlout met letting 1t ge through theusuel setting` stage. pellet'form 'are then dried ,preferably convectively directly as they `come from the4 noduliring` step.

` i 'The Vabove is thepresent preferred method o! carrying out our invention as well gas certain The nodulizing and drying of the modifications.

process mayhowever be embodied in other manners as, for example, in a single rotary drum with lustrated diagrammatically in Fig.- II.

indirect `heating in asteam iacketed drier asil- .In such instance the material is jacket drier. In such modification the preliminary nodulization step occurs in the forepart and end the drum is open to the atmosphereand air flowscountercurrent, thereby maintaining in the iforepart an atmosphere whose temperature and vhumidity is such relative to the temperature and z n 'moisture contentof the material in the nodulizf ing region of the drum that substantially no drying of the material occurs during the nodulization t in the forepartof the drier. In 'the afterpart of 1 nodulesv is raised softhat the relative tempera- T 1 q ture and moisture conditions between 'the atmos` l phere in the drying region of the drum and the the drum,V the temperature of the pre-formed pre-formednodules in` the after part of the drum are such that a. substantial drying atmosphere exists-and the nodules dried.

The system of delivering and feeding as well t as wetting the superphosphate is the same as shown in Fig.\I, and previously described except -nodulization does not occur in the moistener 22.

Instead of -a direct heatdrier, a steam jacketed drier 26 is provdedtwhich is heated with steam in the steam jacket 21, the steam being introduced through pipe 28, stuiling box 29 and spider arm'pipes 30. A vent cock 3l at the charging end of the drier eliminates permanent gases from the inside of the steam jacket, especially venting, the air when Vstarting the drier. Spider. arm pipes 32 `convey away the condensed water by means of a bucket arrangement in the hollow end i ring 33. The condensed water leaves through stuiilnglbox 3l and pipe 35 and goes through an ainpreheatng coil-and then through a steam ytrap to waste. The drieris equipped withlii'ting `varies comprising flat lironst spaced slightly apart as well` as slightiyfaway from the'shell. T he bars are supported every,l ,few feet by means of studs or pins' fastenedftofthe inside Aof ythe drier shell.

Airis delivered ,to the inside of the drier by means of fanti.;` '111ev air is pulled past the air heating coil through duct 38 and vis delivered inside the .stationary drierhead 99. The drier is vented through pipe 40, ian 4l and stack 42; The dried material discharged from the drier falls 4into pit amount of ground phosphate rock is mixed with The nodules of superphosphate in firm first-mois- .tened in a moistener similar to conditioner '2l then fed irogressivelyl through` the, steam to cause any substantial-agglomeration in the conditioner.

- The nodulizing of the superphosphat'e takes place in the upper forepart or feed end of steam drier l29. 'I'he induction and exhaust fans 31 and I] are so regulated tl'iat` the vapor pressure' of water at the feed end is Vsubstantiallyat atmosr pheric pressure. In this part of the drier the material is therefore heated up in a substantially non-drying atmosphere without any drying and the rotation of the drier causes the preliminary nodulation of the superphosphate before drying.

The nodulized superphosphate ir1`,the.form of small pellets is dried at atmospheric pressure in continuous travel through the remaining part of the drier.` Although the material is reasonably strong mechanicallyas it comes from' the drier, it attains further hardness during storage after a day or two.

The aim o( accelerated in this operation. in curve sheets V and VI, where curve (a) representa the original superphosphate untreated by thejpres'ent method and curve (b) represents the treated superphosphate of' the present method.

The following tabulation shows someof the specific analyses:

Trcatedi Untreeted Treated days aiter treatment Two weeks after treatment the treated andthe i untreated materials analyzed as follows: q

Untreated `Treated 'rne eui-ve sheets rigs. v and, vr, giving the curves (a) and' (b) respectively shew that the ,Q25 curing is also attained This is graphically illustrated original superphosphate was 11 days old when treated. This particular type of apparatus is not so effective for treating freshly made 'superphosphate right from the den as a coating builds ,j

up on the steam jacket, which effectively insu'- v latesit and prevents heat transmission, but is effective' on partly cured superphosphate. The" superphosphate" should be at least one week'old and preferably from 10 days totwo weeks old.`

The `quantity o! water required for .moistening the superphosphate is also in this case primarily a function of the age ofthe superphosphate. In

the last mentioned example the quantity of water used was 5.5%. The same original superphosphate treated in the apparatus of Fig. I requires 6.7% water added to the conditioner.. Generally speaking, thequantity of water required in the apparatus of Fig. I isdednitely higher than the 6 y l n y ensayos amount required inthe apparatus of Fig. lI'fwith the same original superphosphate).

In addition to being a function of the age of the original superphosphate used, the quantity of .water reqinred is-also .governed by the particle size or granule ofthe treated material that is desired. If the treated material has a tendency togo to fines, the quantity of water used is increased und if the particle sise-has a tendency lio to get too large the rateo: water mamn n In 'addition to handling straight superphosphate bylmeans of our p 4 we have further discovered that the curing benefit obtained with complete fertilizers is even more pronounced thanr in the case of straight lullerphosphate. Y

When making complete fertiliaerby means of ou:l process the raw materials are preferably mixed before being fed into the conditioner, although the entire mixing operation may be performed in the conditioner.

We have discovered that the curing action. thatis, changing of insoluble P205 to available P205, is inthis case so active that a certain .25 amount of ground phosphate rock added to the mixture will produce available P205.

`Aix-a specific example of making complete fertilizer by means of our process we furnish the following: i `'I'he superphosphate. used analyzed:

Moisture 10.40 Total 19.85

Insoluble PsOs 1.81 Available P20: 18.24 me ma 6.86

The P20 content of the phosphate rock was 33.4%.

To one net ton of superphosphate, 100 lbs. of

40 ground phosphate rock was added, or in other words the weight of the phosphate` rock was 5% ofthe weight of the superphosphate. Stated on a PsOs basis, the weight of the P20; in the phosphate rock was 8.4% of the weight of the total PsOs in the superphosphate.

To the mixture of superphoaphate and phosphate rock was added ammonium-sulphate and potassium chlorideto make the complete mixture contain approximately even amounts of available Themixedmaterialswerenoduliaed intheconditioner 2! with a water addition oi.' 9.3% and directlydriedinthedrierofl"ig .1asabovede 56 The iinkhed treated material vanalysaedas folluws:y

Hoisture t 5.93 Total PIO: 8.94 an insoluble PsOs 0.84 availablem s io Na. '1.80

Exactly why this happens we do not know. The free phosphoric acid present in the superphosphate is not enough to account for this conversion of PzOs'to available form. It is possibly due to the action of monocalcium phosphate or hydrolyzation products of the monocalcium phosphate upon the potassium chloride, which would free some hydrochloric acid which would attack the rock and make it available. No matterwhat reason the fact remains that the P205 is converted to available form.

The physical condition of thetreated complete fertilizer ls of the excellent character of discrete encrusted and indurated nodular globoid'v particles.

The universally practiced method of manufacturing complete fertilizer up to the present time, as described in the beginning of this specification, has beento dry mix the various materials and allow them to set. The set material is milled and the setting and milling operation is often performed twice; In addition to this it is neces sary to add organics to improve the physical condition of the material. 'I'he setting phenomena seem to be due to interaction and recrystallization of the various salts present in the mixture, as for instance monocalcium phosphate and ammonium sulphate forming monoammonium phosphate and calcium sulphate at the contact surfaces between the particles.

By means of our invention all these interactions takeplace during the treatment, so that the resulting granular product is a stable and nonsetting material. The need for the use of organics is also eliminated, which is of considerable economic advantage.

Another significant advantage is that each granule of our complete fertilizer contains all the various plant foods.. This means non-segregation in handling and in distribution on the soil. 'I'he even distribution'of the fertilizer on the neld is of paramount importance fromthe standpoint of maximum crop yields from a minimum amount of fertilizer applied.

Instead of using the nitrogencus and potash containing materials specified in the above given example we may use others, as for instance, nitrate of soda or urea for the nitrogenous material and potassium sulphate or manure salt for the potash containing material. f

'I'he following is an example of the complete fertilizer produced by the method in the apparatus of Fig. II.

The analysis of the superphosphate used was as follows:

Moisture 9.58 Total PzOs 19. 88 Insoluble P205 1. 16 Available PzOs i 18. 7 2 Free acid 5.0`

v The phosphate roer contained 33.4% Pio..

'I'he amount of ground rock used was the same as in the previously given example, that is, 5% by weight of the superphosphate. Am-

monium ysulphate and potassium chloride was mixed with the superphosphate and ground rock to furnish a ratio of approximately This mixture was treated in' accordance with the invention in the apparatus of Fig. 1I and conditioned by adding 7.2% water.

Cil

` content. The method as described in connec-` i i Y i Immediately after` manufacture the 'ilnished material analyzed: t

Moisture is. s2 Total P205..A i p t n Y i 85A Insoluble P205...y i 1.16 Available P1205;.. vi11. 69 N2 i L After 13v days the insoluble P305 had dropped to 0.91%.

From this it will be seen` that approximately 55% of the PzOsin the phosphate rock had been made available immediately, and aftern13 days approximately 80% oi the` P205 in the xiock had been lmade available. l Although the above results described' in connection with Fig. II are fully satisfactory from the standpoint of granular superphosphate, the capacity of such an installation, without duplicaf tion of units or unduly lengthening the drum. is relatively small in comparison to commercial quantities and the area of the zone in which `no dulizing occurs in the forepart off the steam drum is not readily controllable, since the area 1 will uctuate with variationin the character of the superphosphateisuch as its' age or moisture tion with Fig. I is more advantageous since, re-

gardless of the character of the superphosphate, the nodulizing and drying stepsare separately controllable and independently regulable, and products such as those above described in con-` nection with Fig. I were readily obtainable on large scale full capacity operation and in quantitles comparable to commercial production with a single unit as in Fig. I comparable in size with a single unit as illustratgd4 in Fig. II.

' The invention as her] inabove set torthis ern- 4bodied and practiced in particular manners but may be variously embodied and practiced within the scope of the following claims.k 1

lWe claim: 1. A continuous process superphosphate toprcduc'e accelerated curing which comprises ilrst preliminary conditioning a mass of superphosphate by tumbling thesame lin the presence of an aqueous medium in amount v suiiicient to cause nodulization and in a substantially non-drying atmosphere while moving -in a continuous stream through a rotary container at "atmospheric pressure until the massis agglomerated to firm nodules and contains the aqueous ,i medium distributed throughout the same to at least a stage at whichvthere is a tendency to some coalcscence of the agglomerated solid nodules as they issue from the conditioning step, so that the` nodular mass passing thence directly into the drying step may retain a moist'ure content suilicient to inhibitreversion and promote accelerated curing ln the drying step, v.and then directly thereafter heating the preliminarilyfconditioned material, while still in at least such .wetted condition of tending to cause coalescence,

in a drying atmosphere while tumbling theA same "at atmospheric pressure in a stream moving con-V tinuously through a rotaryl container until the product becomes driedyandindurated nodules.

2. A" continuous process o f manufacturing superphosphate to produce accelerated curing which comprises first preliminarily conditioning a mass of freshly prepared den superphosphate by tumbling the 4 same in the presence of an aqueousinedium "in amount suillc'i'en't to cause nodulization and in asubstantially non-drying atof manuifacturingv faraones .t Y. l '7 mosphere while moving in a continuous vstream through a 'rotary container at atmospheric pressure until the mass is agglomerated to firm Inodules andcontains the aqueous medium distributed throughout the same to at least a stage at which there is aV tendency to some coalescence of the yagglomerated solid nodules as they issue from the conditioning step, so that the nodular mass passing thence directly into the drying step may re-l tain a moisture content suiilcient to inhibit re".`-

version and promote accelerated 'curing in the drying step, and then directly thereafter heating,

the preliminarily conditioned material, while still':v `in at least such wetted condition of tending to Vcause coalescence, in a drying atmosphere while tumbling the same at atmospheric pressure in a stream moving continuously through a rotary container until the product becomes dried and indurated nodules.

2i. A continuous process of manufacturing superphosphate to produce accelerated curing which comprises ilrst preliminarily conditioning a mass of partly storage cured den superphosphate `by tumbling the same in 'the presenceof an aqueous `medium in amount suflicient4 to cause nodulizatlon and in a substantiallynon-drying atmosphere while moving in a continuous stream through a rotary container at atmospheric pressure until the mass is agglomerated to firm nodules and contains' the aqueous medium distributed throughout the sameto at least a stag@ at which there is a tendency tb some coalescence of the agglomerated solid nodules as they issue lfrom the conditioning step, so that the nodular mass passing thence directly into the drying step may retain a moisture content suilicient to inhibit reversion and` promote accelerated curing 'in the drying step, and then directly thereafter heat` ing the preliminarly conditioned material, while still in at least such wetted condition of tending to cause coalescence in`a dry atmosphere while tumbling the same at atmospheric pressurein a lstream moving continuously through a rotary container until the product becomes dried and indurated granular nodules.

4. A continuous process of manufacturing complete fertilizer to produce accelerated curing which comprises first preliminarily conditioning a mass of a mixture of superphosphate and other fertilizer ingredients by tumbling the same in the presence of an aqueous medium in amount suflicient to cause nodulization and in a substantially non-drying atmosphere while moving in a continuous stream through a rotary'container -at atmospheric pressure untiithe mass is agglomerated to firm nodules and contains the aqueous ymedium distributed throughout the same to at least a stage at which there is a tendency to some coalescence of the agglomerated solid nodules as they issue from the conditioning step, so that the nodular mass 4passing thence directly into the drying step may retain a moisture content suficient to inhibit reversion and promote accelerated curing in the drying step, and then directly thereafter heating the preliminarily conditioned material, while still in at least such wetted condition of tending to cause coalescence, in a drying atmosphere while tumbling at atmospheric pressure in a stream movingcontinuously through a` rotary container until the product becomes dried and indurated granular nodules. f

5. A method as claimed in claim 1 and in which the heating is eiected by direct contact with hot gasses.

6; a method as claimedin V'claim 1 and in rt p '7. A method as'claimed in claim 1 and in which the preliminary conditioning and the subsequent drying steps axe effected in separate chambers continuously and the preliminarily conditioned material transferred continuously from the conditioning chamber to the drying chamber.

y, 8. The process oi granulating superphosphate 1o which comprises adding water thereto in amount arcanos which the heating is eected byvdirect contact Awith a co-current ow of hot gases.

sutlicient to produce approximately 11%-17% moisture in the resulting mixture, agitating the mixture to produce agglomeration, and ythen tumbling the resulting material in a heated rotary drum until dry hard granules are formed.

WILIAM HAROLD GABELER. ALVIN CHESLEY WILSON. THOMAS ORKNEY TONGUE. MARK SHOELD. 

